Radiation from 10 GeV positrons channeled in silicon crystals

Abstract Radiation from 10 GeV positrons channeled along (110) planes in a 90 μm silicon crystal shows a prominent photon peak at about 50 MeV in agreement with theoretical predictions. The intensity is also in reasonable agreement with expectation. For positrons aligned within ≈20 μ rad to the planar direction, a sharp spectral peak of 25 MeV is also observed, the origin of which is not yet clear. For particles incident at angles near the channeling critical angle of ≈65 μ rad there appears to be structure in the photon spectrum which may correspond to harmonic structure predicted by theory. This is the first observation of such structure for ultrarelativistic particles.